Ch 8 - Precipitation

Question 1

Precipitation

Answer 1

Anything that comes out of a cloud:
Rain
Hail
Snow
Sleet
Drizzle

Question 2

Bergeon-Findeisen Process

Answer 2

Supercooled water droplets attach to ice crystals, bounce around, up and down, get bigger and eventually fall out of the sky as rain

Anywhere above the 0C level

Question 3

Coalescence Process

Answer 3

Temp above 0C, just water droplets, water droplets bounce around getting bigger (depending on connectivity) and eventually fall out of the cloud, much bigger than normal droplets but breaks down before the surface.

Usually forms DZ or -RA

Question 4

DZ Droplets

Answer 4

Less than 0.5mm diameter

Terminal v - 4m/s in still air

Question 5

RA Droplets

Answer 5

0.5/0.6mm in diameter

TV= 9m/s

Question 6

SN

Answer 6

Doesn’t melt, just ice crystals

The closer to 0 you are, the bigger the snow flakes will be (+4–4C biggest snow flakes)

Melt - Freeze - latent heat released, temp dropped, refereeze Repeat

If alt higher than 1500ft it will fall as Sleet or RA

Question 7

Ice Crystals (IC) or diamond dust

Answer 7

Tiny ice crystals floating in atmosphere
Temp has to be below -30
Water vapour that just freezes in the air and floats

Question 8

Snow Grains SG

Answer 8

Small white opaque flat ice grains
Solid precipitation 
Falls from ST clouds 
Hit ground - do not bounce or break 
Frozen DZ

Question 9

Snow Pellets

Answer 9

Snow pellets (tropica snow / groupel)

Conical in shape 2-5mm
Snow like properties
Supercooled water droplets freeze onto snow flakes

Land, bounce and break
Crushable

Question 10

Small Hail GS

Answer 10

Convective type clouds
Soft centre
Covered in transparent layer of ice 
Less than 5mm 
Do not bounce or break on impact

Question 11

Ice Pellets

Answer 11

Solid Ice precip.
Less than 5mm
More spherical 
Snow flakes that have melted and then refrozen
Bounce and break on impact 
Winter months 
Taller cumulus clouds

Question 12

Sleet

Answer 12

Snow flakes that are melting

Mixture of snow and rain

Question 13

Hail (GR)

Answer 13

Solid balls of ice 
Clear or opaque 
5 - 50mm 
Cumulonimbus only to give hail 
Cut in half they have rings which tell you how many melt/referees cycles they have had 
Not common in the tropics 
Overland usually

Question 14

Continuation of Precipitation

Answer 14

Continuous >1hr St

Intermittent <1hr St

Showers SH: rapid start stop of precip usually from Cu type clouds